Cartridge case and method for the manufacture thereof



May 23, 1967 P. 1.. DE LUCA CARTRIDGE CASE AND METHOD FOR THE MANUFACTURE THEREOF 2 Sheets-Sheet Filed Aug. 51, 1965 IN V ENTOR.

y 3, 1967 P. 1.. DE LUCA 3,320,886

CARTRIDGE CASE AND METHOD FOR THE MANUFACTURE THEREOF Filed Aug. 31, 1965 2 Sheets-Sheet 2 Ill nvvnvmn PETER L. De LUCA United States This invention relates to a cartridge case, and more particularly to a new and improved fully combustible cartridge case, and to a method for the manufacture thereof.

It has heretofore been proposed to make cartridge cases for ammunition for weapons out of a combustible material which burns completely upon firing, leaving no residue, thereby eliminating the necessity of extracting the spent cartridge case after firing. While some experiments have been carried out along this line, so far as is known no fully combustible cartridge case has been developed which is practical to manufacture.

Combustible cartridge cases have been made experimentally by accreting nitrocellulose fibers mixed with cellulose fibers from an aqueous suspension on to a porous former. The cartridge cases of this type which have been made generally resemble corresponding cartridge cases made from metals in that they consist of a tubular body which is adapted at one end to receive the base of a projectile and at the other end is provided with a suitable base. The manufacture of such cartridge cases, even experimentally, has involved a number of problems, not the least of which is the sensitivity of nitrocellulose to heat.

It is well known that nitrocellulose lacks stability and various types of stabilizers, especially diphenylamine, have been used with nitrocellulose. Nevertheless, even with such stabilizers precautions must be taken to avoid explosive hazards. In experimental processes heretofore proposed, stabilized nitrocellulose fibers mixed with minor proportions of cellulose fibers have been accreted or felted on a porous former and thereafter given a pre-squeeze with a bag mold in order to remove a part of the water. It has then been proposed to dry the wet cartridge cases containing about 50% water in a tunnel drier at temperatures below 150 F. Afterward the dried case is dipped in a resin solution, further dried under vacuum, placed in a perforated mold, squeezed by application of a rubber molding bag to express the excess resin, then removed from the mold and placed in a vacuum drying chamber maintained at a temperature below about 150 F. After the cartridge case is dry it is trimmed on a lathe. This process is cumbersome and uneconomical. Drying in a tunnel drier causes a dusting problem and therefore involves an explosion hazard. In addition, the process is such that difficulty is encountered in obtaining properly finished cartridge cases which also meet all of the necessary dimensional requirements.

It would be desirable to provide a more practical process for making cartridge cases of the type described from fully combustible materials in which the dimensions of the cartridge case can be predetermined with exactness and the cartridge case can be prepared by a series of steps in a shorter period of time than has heretofore been possible in the experimental type of process previously mentioned and with no greater hazards than heretofore encountered in such experimental process.

One of the objects of the present invention is to provide a new and improved process for making a fully combustible cartridge case which is more practical and economical than processes here described and which results in the production of fully combustible cartridge cases having the desired predetermined dimensions.

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Another object of the invention is to provide a new and improved fully combustible cartridge case made from a plurality of components which can be separately formed in exact dimensions and thereafter assembled.

Other objects and advantages of the invention will appear from the following description in conjunction with the accompanying drawings in which:

FIGURE 1 is a plan view of a new and improved cartridge case provided in accordance with this invention;

FIGURE 2 is a cross sectional view of the cartridge case shown in FIGURE 1 taken along the line 22 of FIGURE 1; and

FIGURE 3 is a cross sectional view of one form of apparatus which can be employed in practicing the process of the invention.

In brief, the new and improved combustible cartridge case provided in accordance with the invention comprises as components a tubular body, a top cap, an annular joining band positioned within said cartridge case and secured to the upper part of said tubular body and the lower part of said top cap and a base having upwardly extending peripheral walls engaging the lower part of said tubular body, all of said components being fully combustible.

The components of the cartridge case are separately formed and thereafter assembled. The tubular body preferably tapers from top to bottom and the upwardly extending peripheral walls of the base preferably should not extend outwardly beyond a vertical plane through the outermost surface of the top of said tubular body. The top cap preferably has side walls which taper from its lower edge to its top and are offset laterally near said lower edge, being thicker adjacent said ofiset area. The construction is preferably also such that the top cap has an annular recess in its inner surface adjacent its lower edge, the tubular body has an annular recess in its inner surface adjacent its upper edge, and said joining band is inlaid in said recesses. The joining band is secured to the top cap and the tubular body by means of a suitable adhesive, for example, an epoxy adhesive, or an adhesive made from nitrocellulose.

The base of the cartridge case is preferably provided with a molded reentrant portion adapted to receive an ignition material. A further feature of the base which is applicable to combustible cartridge cases generally that are made from molded fibrous materials is the provision of an outwardly convex bottom which will resist shrinkage and distortion.

The process of the invention con1prises( a) felting fibers from an aqueous fibrous slurry onto a former or formers having the desired shape of the cartridge case or components of the cartridge case, the fibers in said slurry being fully combustible and containing a major proportion of stabilized nitrocellulose fibers, (b) die drying the resultant article between heated dies at a temperature not exceeding about 250 F. under superatmosphcric pressure while applying suction to said article to remove water, (c) inipregnating the resultant die dried article with a solvent solution of a resin, (d) curing said resin, and (e) restril-zing the cured impregnated article at a temperature not exceeding about 250 F. between dies sized to the final de sired shape while applying suction.

In carrying out this process, the die drying dies used in step (b) and in step (e) are similar except that the dies used in step (b) are slightly oversized whereas the dies used in step (e) correspond to the process dimensions desired in the final article.

Referring to the drawings the combustible cartridge case illustrated in FIGURES 1 and 2 comprises a tubular body 1, a top cap 2, an annular joining band 3 and a base 4 having upwardly extending peripheral walls 5 engaging the lower part 6 of said tubular body 1.

The top cap 2 optionally is provided with an opening 7 through which a projectile is adapted to be fastened to the cartridge case. The side walls 8 and 9 of the top cap 2 taper upwardly and inwardly and are offset laterally at 10 adjacent the lower edge of said top cap 2. It will be seen that the side walls are thicker in the offset area. The inner surface of the top cap 2 adjacent the lower edge is recessed at 11. A recessed area 12 is also provided on the inner surface of the tubular body 1 adjacent its upper edge. The joining band 3 is inlaid in the two recessed areas 11 and 12.

The side wall 13 of the tubular body 1 tapers from top to bottom and the structure is preferably such that the outer surface of the upwardly extending peripheral walls 5 does not project beyond the upper end of the tubular body 1. The bottom surface 14, of the base 4 is outwardly convex. This is desirable in order to prevent any possibility of concavity in the base which might tend to draw the central portion inwardly away from a firing mechanism used in conjunction with the cartridge case. The base 4 has a reentrant portion 15 which forms the space 16 adapted to receive an explosive material or device which can be detonated in order to ignite combustible material placed within the cartridge case. An opening 17 is provided to permit passage of the flame produced by ignition of the detonating material in the chamber 16. The manner in which detonation is accomplished does not form a part of this invention. Another opening 18 is optionally provided in the base 4 for the purpose of filling the cartridge case. This opening can be closed by any suitable type of closure, not shown, after the cartridge case has been filled with a suitable propellant charge. If desired, the opening 18 may be omitted because the propellant charge can be placed in the cartridge case before the base 4 is secured to the tubular body 1.

In FIGURE 3 a pair of die drying dies is illustrated. These dies consist of a male die 10 and a female die 20. These dies have flanges 21 and 22, respectively, which are separated from each other when the dies are closed by a vacuum ring 23.

The male die 19 is provided with a heating chamber 24 into which steam, hot oil or other suitable heat exchange medium, can be introduced through an inlet 25 and withdrawn through an outlet 26. The male die 19 is also provided with an annular vacuum chamber 27 which is connected by pipes 28 and 29 to a suitable vacuum pump, not shown. The vacuum chamber 27 is connected by a number of passageways 30 to an annular recessed area 31 on the upper surface of the flange 21 of the male die 10.

An annular recessed area 32 is provided in the lower part of the female die 20 which is connected by drainage passageways 33 in vacuum ring 23 to the recessed area 31 and thence through passageways 30 to the suction chamber 27.

The female die 20 is provided with a heat exchange chamber 34 into which a heat exchange medium, such as steam, hot oil, or the like, can be introduced through inlet 35 and withdrawn through outlet 36.

The structure described is mounted in any suitable manner so that the dies 19 and 20 can be brought together under pressure with the felted article 37 between them. In the embodiment of the invention illustrated in FIG- URE 3, the felted article is the base 4 of the cartridge case. The other components of the cartridge case are die dried in a similar manner using dies of appropriate shape.

The male die 19 preferably comprises a brass screen with openings therein large enough to permit the passage of water, but small enough to prevent the passage of fibers. The solid portion of the die which supports the screen contains grooved passageways to permit the water which is removed from the article that is being dried to drain away into the vacuum chamber 27. The female die is solid and it is preferably chrome plated thereby giving the finished article a smooth outer surface.

As previously indicated, it is desirable to use two sets of dies for die drying the various components of the cartridge case. The first set of dies is slightly oversize and the second set of dies are formed to give an article having the exact dimensions desired in the final article. By making the first set of dies slightly oversize, it is possible to compensate for shrinkage.

The invention will be further illustrated but is not limited by the following example in which the quantities are given by weight unless otherwise indicated.

Example A slurry is prepared by dispersing nitrocellulose fibers and kraft cellulose fibers together with diphenylamine in water to give a stock consistency of 0.4% (fiber to water). The proportions employed are such that the nitrocellulose fibers constitute and the kraft cellulose fibers 15% of the total fiber content. The diphenylamine is 1.75% of the total fibers.

The components of the cartridge case are felted from said aqueous slurry onto porous formers having the shapes of the respective components and the felted components are then die dried between dies of the type previously described, heated to a temperature of about 250 F. under a pressure of about pounds per square inch for a period of time from 2 to 6 minutes, depending upon the particular component. The wall thickness of the body component can be varied, for example, from about /8 inch to A inch. The other components will normally have a corresponding wall thickness, except the joining band which is somewhat thinner, and in most cases is about /2 the wall thickness of the body component.

As a specific illustration, in one type of cartridge case where the body component weighs 200 grams, the cap component will weigh 70 grams, the joining band component will weight 25 grams, and the base component about 50 grams. All of these weights are on a dry basis.

After the felting step and the first die drying step, each of the components is immersed in a resin impregnating bath. A suitable bath consists of 2 pounds polyvinylformal resin, (e.g., Formvar 7/95S) dissolved in 23 pounds of a mixture of ethanol and toluene containing 40% ethanol and 60% toluene. Optionally, a nitrocellulose stabilizer, for example, 50 grams of diphenylamine can be added to this bath.

The various components of the cartridge case are dipped in the impregnating bath for a period of one to two minutes and are then allowed to cure by air drying at room temperature (e.g., 75 F.) for a period of about 12 hours. This period will vary, depending upon the particular component.

After the component is substantially dry to touch it is placed in a second pair of die drying dies having the desired final dimensions and the dies are closed for a period of five seconds. The second pair of die drying dies are heated to a temperature of about 250 F.

In both the first pair of die drying dies and the second pair of die drying dies suction is applied to the component part through the male die.

The vacuum applied to the drying dies can vary but is preferably 2028 inches of mercury.

The nitrocellulose fiber is available commercially and normally contains. 10-14% nitrogen. Nitrocellulose containing 12-13% nitrogen is preferred.

The impregnating resin can be any resin which is compatible with the propellant and is water insoluble when cured. The resin serves to enhance the strength of the cartridge case and provide water resistance. The proportion used preferably should not destroy the porosity of the molded fiber case because the porosity assists in combustion of the ease. Usually the resin content of the case will be 10% to 25%, preferably 152-0%, by weight of the case.

The joining band is secured to the upper part of the body by using a suitable adhesive. Similarly, the top cap is secured to the joining band. In a like manner the base can be secured to the body.

A suitable adhesive can be prepared, for example, by mixing 17.6% nitrocellulose (grade DHAST), 12.4% oamphor and 70% acetone. Other suitable adhesives are the epoxy adhesives.

The various components of the case can have different nitrocellulose contents. Thus, the body can be higher in nitrocellulose than the joining band and the top cap thereby providing more rapid combustion in the body area. Usually, the quantity of nitrocellulose should be within the range of 6.5% to 90% by Weight of the total fibers, the remainder being cellulose or other fibers which will burn. Due to the high combustibility of the nitrocellulose and the erosion by-products of combustion, the

other fibers such as cellulose are also rapidly consumed.

The body and top cap can be molded as a single piece thereby eliminating the forming band but this is a more diflicult operation than molding the components separately. More rejects are produced and it is not possible to vary the nitrocellulose content in various portions of the cartridge case.

The invention provides a new and improved combustible cartridge case and a new and improved process for producing a combustible cartridge case in which the dimensions can be predetermined with exactnes and the production time can be reduced. Surprisingly, by the practice of the process no great hazards have been encountered during the die drying steps.

The invention is hereby claimed as follows:

1. A combustible cartridge case comprising as components a tubular body, a top cap, an annular joining band positioned within said cartridge case and secured to the upper part of said tubular body and the lower part of said top cap, and a base having upwardly extending peripheral walls engaging the lower part of said tubular body, all of said components of said cartridge case being fully combustible.

2. A cartridge case as claimed in claim 1 in which said components contain a major proportion of stabilized ni trocellulose fibers.

3. A cartridge case as claimed in claim 2 in which the proportion of nitrocellulose is higher in the body than in said joining band and said top cap.

4. A cartridge case as claimed in claim 1 in which said body tapens from top to bottom.

5. A cartridge case as claimed in claim 4 in which the outer surface of the upwardly extending peripheral walls of said base do not extend outwardly beyond a vertical plane through the outermost surface of the top of said tubular body.

6. A combustible cartridge case as claimed in claim 1 in which said top cap has sidewalls which taper from its lower edge toward its top and are offset laterally near said lower edge, being thicker adjacent said offset area.

7. A combustible cartridge case as claimed in claim 1 in which said top cap has an annular recess in its inner surfiace adjacent its lower edge, said tubular body has an annular recess in its inner surface adjacent its upper edge, and said joining band is inlaid in said recesses.

8. A combustible cartridge case comprising a tubular body of molded fibrous material, a top cap united with said body, and a base of molded fibrous material, said cartridge case being fully combustible and said base being convex outwardly whereby the central part of said base extends outward and slopes gradually toward the edges.

9. A process of making a combustible cartridge case which comprises: (a) felting fibers from an aqueous fibrous slurry on to a former having the shape of a cartridge case, the fibers in said slurry being fully combustible and containing a major proportion of stabilized nitrocellulose fibers, (b) die drying the resultant article between heated dies at a temperature not exceeding about 250 F. under superatmospheric pressure While applying suction to said article to remove water, (c) impregnating the resultant die dried article with a solvent solution of a resin, (d) curing said resin, and (e) restriking the cured impregnated article at a temperature not exceeding 250 F. between dies sized to the final desired shape while applying suction.

10. A process as claimed in claim 9 in which a nitrocellulose stabilizing agent is added to said solvent solution of said resin.

References Cited by the Examiner UNITED STATES PATENTS 1,329,503 2/1920 Casey 102-97 1,625,631 4/1927 Spotswood et al 10297 3,218,907 11/1965 Beal et al. 102-43 X BENJAMIN A. BORCHELT, Primary Examiner. ROBERT F. STAHL, Examiner. 

1. A COMBUSTIBLE CARTRIDGE CASE COMPRISING AS COMPONENTS A TUBULAR BODY, A TOP CAP, AN ANNULAR JOINING BAND POSITIONED WITHIN SAID CARTRIDGE CASE AND SECURED TO THE UPPER PART OF SAID TUBULAR BODY AND THE LOWER PART OF SAID TOP CAP, AND A BASE HAVING UPWARDLY EXTENDING PERIPHERAL WALLS ENGAGING THE LOWER PART OF SAID TUBULAR BODY, ALL OF SAID COMPONENTS OF SAID CARTRIDGE CASE BEING FULLY COMBUSTIBLE. 